Bead blasting + anodizing aluminum for cosmetic finish (a la Apple)

Hi everyone,

I'm working on an aluminum enclosure for a consumer electronics device that requires a satin aluminum finish, much like that on Apple's MacBooks and iPhones. After machining, the part is tumbled for deburring, bead blasted with glass beads, then anodized. The trouble we're running into is at the bead blasting stage.

We've had two samples run, one with #10 glass beads at ~50 psi (below left), the other with #8 glass beads at an unknown pressure, plus Type II clear anodizing (below right).



It's not as obvious in the image but the #8 blasted finish is significantly duller (less of that reflected light hotspot) and has this awful chalkboard texture that's very unpleasant to the touch. On the other hand, the #10 blasted finish is much better and borderline acceptable, but still not quite up to the beautifully smooth texture on iPhones and MacBooks.

Which brings me to my question—does anyone with experience finishing aluminum parts in a similar fashion have any advice on grades and pressures? I've read on parts of the internet that Apple used to use a #6 bead blast, but is now using a #8 bead blast on newer products, but based on our tests, I can't seem to figure out how that can be. Could the underlying finish matter? In Apple's aluminum watch video, they seem to buff the parts before bead blasting, which sort of makes sense but seems extraneous if the machining marks are relatively light.

Thanks for all the help!

You need a really good anodize provider to work with you for a consistent process. You might have to ensure you always use the same grade and vendor for the raw aluminum, as different batches or H/T may give varying results. Even the tumbling may cause issues if you use media that's also been exposed to other metals besides the Al you're using, as it could contaminate the surface of the part.

Do you spec an etch prior to anodize? Might even be worth trying etch, BB, light etch, anodize to ensure a clean, consistent surface. If these will be made in the thousands or more, look at semi-robotizing the BB, use a turntable with a BB nozzle that moves or oscillates a specified amount over time. Make sure workers have clean cotton gloves on, any skin oils could show up afterwards.

If need be contact more local service providers, you might luck into one that's worked with Apple already, and has the method down cold. Even if the can't (shouldn't) do the exact method spec'd for Apple, they should have a similar "generic" process they can use.

Initial finish is really important. For #10 i sand with a small orbit orbital sander too 220. All that bead blasting does is hide stuff so you have to have nothing to hide.
Check into vapor blasting. The finish is significantly better with the same bead size.
Jordy

Sent from my LG-H831 using Tapatalk

I have, let's just call it significant experience figuring out how to finish 6061 to Apple standards.

First off the bat? You can't. This isn't me trying to be flippant, but Apple struggles with finishing internally... and they have every finishing supplier on the planet doing whatever it takes to get a PO. Whenever I meet up with my Apple friends, they are *always* lamenting finishing issues that they are trying to solve or processes they are having trouble controlling

Now, you can get close (and with a lot of effort, *very* close), but Apple's standards for product that ships are absurdly high and yes, Apple's fetishist fans do notice if the stuff you ship is in the uncanny valley of good, but not quite there (and that's bad if you're selling accessories, because it's the Apple fetishists who are the ones who will be promoting the hell out of your product on one of the 15,202 Apple forums and blogs and podcasts).

Second? Tumbling isn't good enough. You need great finishes off the machine or initial forming process, and a lite tumble... but every bead blasted Apple surface starts as a polished surface. Go pick through their handful of manufacturing videos and not the obsessive efforts they go through to polish stuff at scale. Lots of robotic polishing, special fixtures, even custom molded nylon plugs to keep edges perfect.

Finally? You need to be working with the top 10% of anodizers out there, and you're going to write off at least 30 units with them trying to get the process nailed for your particular parts, per color. Such anodizers are already expensive outfits to work with, but expect them to charge a premium on top of that. Even so, you're going to have a high scrap rate (expect to start out shoving about 10% of your first production run to ding-n-dent sales, but you should quickly move to a mere 3%-5%).

Most Apple accessory makers have given up and now use plating/painting processes. It gets close enough to Apple's finishes that nobody notices, and is just about the only way to do accessories, at scale, while maintaining the absurd margins that distributors and retail requires.

As noted above, finish off the machine is crucial, IMO.
Also, matching exactly their finish is going to be a bit of an exercise.
I've had some success at times by playing with different tumbling media, length of time. I get a fair amount of parts hard ano'd.
Good luck!

Finish off machine is critical as others have stated. Surface should be polished before blasted and blasting should be done at the lowest pressure possible. 50 is way too high. I have never blasted aluminum above 40. Start low and work up, you cant go backwards. Try setting up your own anodize for some trials.

Thanks for all the feedback everyone!

Milland said:

Do you spec an etch prior to anodize? Might even be worth trying etch, BB, light etch, anodize to ensure a clean, consistent surface. If these will be made in the thousands or more, look at semi-robotizing the BB, use a turntable with a BB nozzle that moves or oscillates a specified amount over time. Make sure workers have clean cotton gloves on, any skin oils could show up afterwards.

If need be contact more local service providers, you might luck into one that's worked with Apple already, and has the method down cold. Even if the can't (shouldn't) do the exact method spec'd for Apple, they should have a similar "generic" process they can use.

Click to expand...

The process used to produce the part on the right included a 2-3 minute etch. We spoke with the anodizer today and the etch and the 30 minute anodizing bath may be the biggest contributor to the dullness. We'll have to run some more samples, though. Our BB place actually has one of those indexable turntable blasting cabinets but we wanted to nail down the finishing recipe before committing to custom fixtures.

We're in the SF Bay Area so a few anodizing places we looked into actually list Apple as a client, but the issue with anodizing shops in the area is that they're almost 100% geared towards satellite parts and medical, so the quotes we got back were between 3x to 5x what shops in the Midwest were quoting. We just don't have those kinds of margins, and Apple probably uses local shops only for prototypes too, so even they likely pay less for bead blasting and anodizing.

Jorgo said:

Initial finish is really important. For #10 i sand with a small orbit orbital sander too 220. All that bead blasting does is hide stuff so you have to have nothing to hide.
Check into vapor blasting. The finish is significantly better with the same bead size.
Jordy

Sent from my LG-H831 using Tapatalk

Click to expand...

Thanks for the feedback!

gkoenig said:

I have, let's just call it significant experience figuring out how to finish 6061 to Apple standards.

First off the bat? You can't. This isn't me trying to be flippant, but Apple struggles with finishing internally... and they have every finishing supplier on the planet doing whatever it takes to get a PO. Whenever I meet up with my Apple friends, they are *always* lamenting finishing issues that they are trying to solve or processes they are having trouble controlling

Now, you can get close (and with a lot of effort, *very* close), but Apple's standards for product that ships are absurdly high and yes, Apple's fetishist fans do notice if the stuff you ship is in the uncanny valley of good, but not quite there (and that's bad if you're selling accessories, because it's the Apple fetishists who are the ones who will be promoting the hell out of your product on one of the 15,202 Apple forums and blogs and podcasts).

Second? Tumbling isn't good enough. You need great finishes off the machine or initial forming process, and a lite tumble... but every bead blasted Apple surface starts as a polished surface. Go pick through their handful of manufacturing videos and not the obsessive efforts they go through to polish stuff at scale. Lots of robotic polishing, special fixtures, even custom molded nylon plugs to keep edges perfect.

Finally? You need to be working with the top 10% of anodizers out there, and you're going to write off at least 30 units with them trying to get the process nailed for your particular parts, per color. Such anodizers are already expensive outfits to work with, but expect them to charge a premium on top of that. Even so, you're going to have a high scrap rate (expect to start out shoving about 10% of your first production run to ding-n-dent sales, but you should quickly move to a mere 3%-5%).

Most Apple accessory makers have given up and now use plating/painting processes. It gets close enough to Apple's finishes that nobody notices, and is just about the only way to do accessories, at scale, while maintaining the absurd margins that distributors and retail requires.

Click to expand...

Hi Greg! I thought I recognized your username from somewhere. I followed your blog after the Mac Pro post, and having someone pore through their manufacturing videos and confirm what I'm seeing is fantastic.

I completely understand that one simply can't make products to Apple's quality standards without either a significant investment in process development or a significant per unit cost to make up for high reject rates and refinishing. I'm willing to settle for less, though, and thankfully this product isn't an Apple accessory. Still, I'm hoping I can get 95% of the way there with some experimentation.

I noticed that the aluminum watch video shows the machined enclosure being polished before blasting, which leads me to another observation. Apple's finishes seem to have gotten a lot finer recently. My iPhone 6S has a much finer finish compared to the one on my 2012 MacBook Pro, and I suspect polishing may be necessary for the newer finish—which is fine because achieving the old finish would be more than satisfactory.

I think we'll continue experimenting with blasting and anodizing, despite the difficulties. At low quantities (hundreds), we're being quoted around $1.20 for blasting and anodizing (local shops in the SF Bay Area are $3+). With more volume, we can switch to semi-automated blasting and we can develop our own racks, which should push that price down by at least another 20-30%.

eaglemike said:

As noted above, finish off the machine is crucial, IMO.
Also, matching exactly their finish is going to be a bit of an exercise.
I've had some success at times by playing with different tumbling media, length of time. I get a fair amount of parts hard ano'd.
Good luck!

Click to expand...

Thanks for the feedback! Do you have any specific recommendations for grades/pressures and etch/anodize times?

MaxPrairie said:

Finish off machine is critical as others have stated. Surface should be polished before blasted and blasting should be done at the lowest pressure possible. 50 is way too high. I have never blasted aluminum above 40. Start low and work up, you cant go backwards. Try setting up your own anodize for some trials.

Click to expand...

Unfortunately, due to cost and geometry limitations, polishing is just out of the question. Am I incorrect in my assumption that a part with a good machine finish with a light tumble in plastic media will be sufficient to achieve relatively smooth cosmetic bead blasted finish?

If the surfaces you are concerned with are machined, get some PCD inserts. They are expensive, but they last forever. Jack the surface speed way up, use a large radius insert, and you should have a mirror finish right off the machine.

Javelin said:

Hi everyone,

I'm working on an aluminum enclosure for a consumer electronics device that requires a satin aluminum finish, much like that on Apple's MacBooks and iPhones. After machining, the part is tumbled for deburring, bead blasted with glass beads, then anodized. The trouble we're running into is at the bead blasting stage.

We've had two samples run, one with #10 glass beads at ~50 psi (below left), the other with #8 glass beads at an unknown pressure, plus Type II clear anodizing (below right).

It's not as obvious in the image but the #8 blasted finish is significantly duller (less of that reflected light hotspot) and has this awful chalkboard texture that's very unpleasant to the touch. On the other hand, the #10 blasted finish is much better and borderline acceptable, but still not quite up to the beautifully smooth texture on iPhones and MacBooks.

Which brings me to my question—does anyone with experience finishing aluminum parts in a similar fashion have any advice on grades and pressures? I've read on parts of the internet that Apple used to use a #6 bead blast, but is now using a #8 bead blast on newer products, but based on our tests, I can't seem to figure out how that can be. Could the underlying finish matter? In Apple's aluminum watch video, they seem to buff the parts before bead blasting, which sort of makes sense but seems extraneous if the machining marks are relatively light.

Thanks for all the help!

Click to expand...

Any luck getting the Apple finish? I'm having the same issues with the chalking like texture after polish, bead blast and anodizing.